A small-diameter hydrogen circuit moisture flow measurement method

Abstract

This invention relates to a method for measuring the flow rate of wet gas in a hydrogen loop, characterized by the following steps: acquiring capacitance timing signals and ultrasonic timing signals based on an ultrasonic sensor and a capacitance sensor; converting the capacitance sensor timing signals into relative capacitance change (RCD); obtaining the forward and reverse flow transit times using the ultrasonic sensor timing signals; calculating the ultrasonic wet gas flow rate; determining the boundary value for correcting the gas phase flow rate at high cross-sectional moisture content using a drift model; judging whether the RCD is less than the determined boundary value; and, based on the judgment result, performing different steps and using different measurement models to calculate the flow rate of wet gas in the hydrogen loop.

Description

Technical Field

[0001] This invention belongs to the field of moisture flow measurement and relates to a method for measuring moisture flow in small-diameter pipes based on ultrasonic and electrical dual-mode. Background Technology

[0002] Hydrogen fuel cell vehicles offer significant advantages over traditional vehicles in terms of energy conservation and environmental protection. However, hydrogen is not completely consumed during the power generation process and unreacted hydrogen needs to be recycled through a circulation loop. Water is a byproduct of the power generation reaction, and it is difficult to completely drain during battery operation, flowing at high speed in the loop as moisture. Excessive liquid content can lead to blockages or water hammer, necessitating real-time monitoring of the moisture flow rate within the circulation loop to ensure the efficient and stable operation of the hydrogen fuel cell.

[0003] Traditional methods for measuring moisture flow primarily use single-phase flow meters, or they can be combined with classic flow instruments such as differential pressure flow meters. However, most single-phase flow meters interfere with the normal flow of fluid and cause pressure loss, and the measurement results have poor repeatability, making it difficult to meet the requirements for accurate moisture measurement in hydrogen fuel cell circuits.

[0004] Methods for measuring moisture content mainly include the quick-closing valve method, X-ray attenuation method, optical method, and ultrasonic method. The quick-closing valve method interferes with fluid flow and cannot perform real-time, online moisture content measurement. The X-ray attenuation method is costly and poses safety hazards. The optical method uses a high-speed camera to photograph the flow state inside the pipe and uses calibration methods as a reference to determine the phase content of the fluid within the pipe. It requires high calibration accuracy and methods, and the pipe must be made of transparent material, making it unsuitable for small-diameter hydrogen circulation loops. The ultrasonic method measures phase content by utilizing the different attenuation levels of ultrasonic waves propagating in different fluids, but it suffers from drawbacks such as weak received signal energy, low signal-to-noise ratio, and poor accuracy in moisture content measurement.

[0005] In summary, there is an urgent need to propose a non-contact, undisturbed, high-precision, and fast-response method for measuring the flow rate of humidified gas in small-diameter hydrogen circulation loops. Summary of the Invention

[0006] This invention proposes a method for measuring the flow rate of moist gas in a small-diameter hydrogen circuit. It utilizes an ultrasonic sensor to measure the flow rate of moist gas and a capacitive sensor to measure the moisture content. Based on the analysis of the influence of liquid phase distribution on gas flow rate measurement, it integrates acoustic and electrical measurement information to establish a more accurate measurement model for moist gas flow parameters. The technical solution is as follows:

[0007] A method for measuring the wet gas flow rate in a hydrogen loop includes the following steps: acquiring capacitance time-series signals and ultrasonic time-series signals based on ultrasonic and capacitance sensors; converting the capacitance sensor time-series signals into relative capacitance change (RCD); obtaining the forward and reverse flow transit times using the ultrasonic sensor time-series signals; calculating the ultrasonic wet gas flow rate; determining the boundary value for correcting the gas phase flow rate at high cross-sectional moisture content using a drift model; judging whether the RCD is less than the determined boundary value; and, based on the judgment result, performing different steps and using different measurement models to calculate the wet gas flow rate in the hydrogen loop.

[0008] The specific steps are as follows:

[0009] Step 1: Based on ultrasonic and capacitive sensors, acquire two-phase pressure P, two-phase temperature T, capacitive sensor time-series signal v(t), and ultrasonic sensor time-series signal s(t);

[0010] Step 2: Calculate the gas density ρ using the two-phase pressure P and the two-phase temperature T respectively. g and liquid density ρ l The timing signal of the capacitance sensor is converted into a relative capacitance change RCD using formula (1), and the trans-current transit times t1 and t2 are obtained from the timing signal of the ultrasonic sensor:

[0011]

[0012] Among them, V g and V w These are the voltage values ​​measured when the pipe is empty and full of water, respectively.

[0013] Step 3: Calculate the ultrasonic moisture gas flow rate Q using formula (2). tp :

[0014]

[0015] Where A is the cross-sectional area of ​​the pipe, L is the distance between the two ultrasonic probes of the ultrasonic sensor, θ is the angle between the ultrasonic sensor and the central axis of the pipe, and K c This is a correction factor;

[0016] Step 4: Determine the boundary value and check if RCD is less than the determined boundary value. If RCD is less than the boundary value, proceed to Step 5; otherwise, proceed to Step 6.

[0017] Step 5: Determine if the pipe is a vertical pipe. If it is a vertical pipe, calculate the flow rate Q of the moist gas using formula (3). g ;

[0018]

[0019] Where γ is the fraction of the pipe cross-sectional area occupied by the entrained droplets in the center of the pipe, and α under the vertical pipe is obtained from formula (4):

[0020]

[0021] Where D is the pipe diameter and δ0 is the liquid film thickness;

[0022] If it is a horizontal pipe, the flow rate Q of the moist gas can be calculated using formula (5). g :

[0023]

[0024] Where θ′ is half of the central angle corresponding to the gas-liquid interface, calculated by formula (6):

[0025]

[0026] Where R is the pipe radius, δ0 is the liquid film thickness, and α under the horizontal pipe is obtained by the following formula:

[0027]

[0028] Step 6: When RCD is greater than the boundary value, α is determined by formula (8):

[0029]

[0030] Where K1 and K2 are the coefficients to be fitted, Q l This refers to the liquid phase flow rate;

[0031] Determine whether the pipe is a vertical pipe. If it is a vertical pipe, calculate the flow rate Q of the moist gas by combining formulas (4) and (8). g .

[0032] Furthermore, in the third step, K c It is 1.12;

[0033] Furthermore, in the fourth step, the boundary value is 28.9%.

[0034] Furthermore, in step six, K1 and K2 are set to 1.14 and 5.06, respectively.

[0035] According to the above method, this invention realizes the measurement of small-diameter moist gas flow rate and has the following advantages:

[0036] (1) It can realize the measurement of moisture gas flow rate.

[0037] Using information from the ultrasonic-electric dual-mode, a measurement model for the flow rate of moist gas in vertical and horizontal pipes was established to obtain the actual gas flow rate.

[0038] (2) Achieve measurement of wet gas flow rate at high moisture content

[0039] By using a drift model to correct the measurement results of moist gas flow rate at high moisture content, the measurement of moist gas flow rate at relatively high moisture content was realized.

[0040] (3) Simple, low-cost, online measurement

[0041] Moisture gas flow rate can be measured by using ultrasonic and capacitive sensors to measure relevant parameters. This method is simple to operate, low in cost, and can be performed online.

[0042] (4) High measurement accuracy

[0043] Gas flow rate was measured using this method under humid conditions. The average relative error was 3.92% for the vertical pipe and 4.62% for the horizontal pipe. Attached Figure Description

[0044] Figure 1 Flowchart for Moisture Gas Flow Measurement

[0045] Figure 2 Relationship between liquid film thickness δ and gas content α in vertical pipe

[0046] Figure 3 Relationship between liquid film thickness δ and gas content α in a horizontal pipe

[0047] Figure 4 Schematic diagram of measurement error of gas phase volumetric flow rate in vertical pipe

[0048] Figure 5 Schematic diagram of error in horizontal pipe gas phase volumetric flow rate measurement Detailed Implementation

[0049] The present invention will now be further described in conjunction with the accompanying drawings and embodiments:

[0050] This embodiment describes a method for measuring the flow rate of moist gas based on ultrasonic and capacitive sensors. The specific implementation in the moisture measurement is as follows: The operating pressure is adjusted to 101 kPa, the gas phase flow rate is 56 L / min to 150 L / min, the liquid phase flow rate is 2.5 L / min to 5.5 L / min, and the pipe diameter is a fixed value D = 10 mm. Signal acquisition includes the operating pressure P output by the pressure sensor, the operating temperature T output by the temperature sensor, the ultrasonic time-series signal s(t) output by the ultrasonic sensor, and the capacitive time-series signal v(t) output by the capacitive sensor. The sampling frequency of s(t) is 8 MHz, the sampling time for each data set is 10 s, and v(t) is a 330 kHz sine wave signal with a sampling frequency of 200 kHz.

[0051] The method proposed in this invention utilizes ultrasonic and capacitive sensors to measure relative capacitance changes and uncorrected gas flow rates, respectively. Measurement models for vertical and horizontal pipes were established, and the gas flow rate at high cross-sectional moisture content was corrected using a drift model. Ultimately, the method achieves the measurement of humid gas flow rates within a relatively high moisture content range.

[0052] Using ultrasonic and capacitive sensors, the gas flow rate of moist gas under different flow conditions is calculated through different measurement models. The specific calculation steps are as follows:

[0053] Step 1: Collect two-phase pressure P, two-phase temperature T, time-series signal v(t) from the capacitive sensor, and time-series signal s(t) from the ultrasonic sensor;

[0054] Step 2: Calculate the gas density ρ using operating conditions P and T respectively. g and liquid density ρ l The capacitance timing signal is converted into a relative capacitance change RCD using formula (1), and the trans-current transit times t1 and t2 are obtained using the ultrasonic signal:

[0055]

[0056] Among them, V g and V w These are the voltage values ​​measured when the pipe is empty and full of water, respectively. The transit times t1 and t2 of the ultrasonic signal in both directions are obtained using the cross-correlation method.

[0057] Step 3: Calculate the ultrasonic moisture gas flow rate Q using formula (2). tp :

[0058]

[0059] Where A is the cross-sectional area of ​​the pipe, θ is the angle between the ultrasonic sensor and the central axis of the pipe, and K c The correction factor is set to 1.12 within the experimental range.

[0060] Step 4: Based on the empirical value of the boundary value w obtained from the experiment, in this embodiment, w = 28.9% is selected. It is determined whether RCD is less than 28.9%. If RCD is less than 28.9%, that is, the moisture content is less than 33%, the measurement result of the capacitance sensor is directly used, and step 5 is performed. When RCD is greater than 28.9%, the effect of the drift model on the capacitance measurement value is used to correct it, and step 6 is performed.

[0061] Step 5: When RCD is less than 28.9%, first determine whether the pipe is a vertical pipe. If it is a vertical pipe, calculate the wet gas flow rate Q using formula (3). g .

[0062]

[0063] Where γ is the fraction of the pipe cross-sectional area occupied by the entrained droplets in the center of the pipe, and α under the vertical pipe can be obtained by formula (4):

[0064]

[0065] Where D is the pipe diameter and δ0 is the liquid film thickness.

[0066] If it is a horizontal pipe, the flow rate Q of the moist gas can be calculated using formula (5). g :

[0067]

[0068] Where θ′ is half of the central angle corresponding to the gas-liquid interface, such as Figure 3 As shown. Calculated using formula (6):

[0069]

[0070] Where R is the pipe radius, δ0 is the liquid film thickness, and α under a horizontal pipe can be obtained from the following formula:

[0071]

[0072] Step 6: When RCD is greater than 28.9%, according to the modified model, α can be determined by formula (8):

[0073]

[0074] Where K1 and K2 are the coefficients to be fitted, and are taken as 1.14 and 5.06 respectively, Q... l Let Q be the liquid phase flow rate. In humid applications, the liquid phase flow rate is Q. l Relative to moisture flow rate Q g The value is relatively small and does not change much, thus having a small impact on actual measurement results. Given Q... l In the case of or Q l If the pipe is kept within a certain known range, first determine whether it is a vertical pipe. If it is a vertical pipe, then use formulas (4) and (8) to calculate the flow rate Q of the moist gas. g .

[0075] Based on the above method, the measurement of wet gas flow rate in small-diameter pipes was finally achieved.

[0076] In this example, based on the above method, the measurement of moist gas flow rate was finally achieved. Verification showed that the proposed ultrasonic-electrical dual-mode moist gas flow rate measurement method had an average measurement error of 3.92% for vertical pipes and 4.62% for horizontal pipes at different pipe angles (see attached figure). Figure 4 and attached Figure 5 ), where measurement error = (measured value - true value) / true value × 100.

[0077] This invention establishes moisture flow measurement models for both vertical and horizontal pipes, and corrects the ultrasonic flow measurement results using capacitance measurements. A drift model is then used to further correct the moisture flow measurement at high moisture content. Ultimately, this method achieves the measurement of moisture gas flow within a relatively high moisture content range. It is simple to operate, low in cost, and has a wide measurement range. It enables real-time, online, high-precision measurement.

[0078] Step 5: Determine the relative capacitance change (RCD). Check if RCD is less than 28.9%. If it is less than 28.9%, further determine if it is a vertical pipe. If it is a vertical pipe, then the moisture gas flow rate Q... g for:

[0079]

[0080] If it is a horizontal pipe, the flow rate of the moist gas is Q. g for:

[0081]

[0082] Where θ′ is half of the central angle of the horizontal pipe wavy flow interface, such as Figure 3 As shown:

[0083]

[0084] Where R is the pipe radius and δ0 is the liquid film thickness, the relationship with α is as follows:

[0085]

[0086] If it is greater than 28.9%, then the moisture gas flow rate Q g The value of α in the calculation formula should be:

[0087]

[0088] Where K1 and K2 are the coefficients to be fitted, and are taken as 1.14 and 5.06 respectively;

[0089] Based on the above method, the measurement of wet gas flow rate in small-diameter pipes was finally achieved.

[0090] In this example, based on the above method, the measurement of moist gas flow rate was finally achieved. Verification showed that the proposed ultrasonic-electrical dual-mode moist gas flow rate measurement method had an average measurement error of 3.92% for vertical pipes and 4.62% for horizontal pipes at different pipe angles (see attached figure). Figure 4 and attached Figure 5), where measurement error = (measured value - true value) / true value × 100.

[0091] This invention establishes moisture flow measurement models for both vertical and horizontal pipes, and corrects the ultrasonic flow measurement results using capacitance measurements. A drift model is then used to further correct the moisture flow measurement at high moisture content. Ultimately, this method achieves the measurement of moisture gas flow within a relatively high moisture content range. It is simple to operate, low in cost, and has a wide measurement range. It enables real-time, online, high-precision measurement.

Claims

1. A method of measuring moisture flow in a hydrogen circuit, characterized by, The process includes the following steps: acquiring capacitance timing signals and ultrasonic timing signals based on ultrasonic and capacitance sensors; converting the capacitance sensor timing signals into relative capacitance changes. RCD The trans-current and counter-current transit times are obtained using the time-series signal from the ultrasonic sensor; the ultrasonic moisture gas flow rate is calculated; the boundary values ​​for correcting the gas phase flow rate using the drift model at high cross-sectional moisture content are determined, and the judgment is made. RCD Whether it is less than the determined boundary value, different steps are performed based on the judgment result, and different measurement models are used for calculation to realize the measurement of hydrogen circuit moisture flow rate. The method is as follows: First step: Collecting two-phase pressure, two-phase temperature, capacitive sensor timing signal, and ultrasonic sensor timing signal based on ultrasonic sensor and capacitive sensor P T ;​​​ Second step: by two-phase pressure P , two-phase temperature T Gas density and liquid density are calculated separately RCD Converts the capacitance sensor time series signal into relative capacitance change Obtains the forward and reverse flow transit times and in, and These are the voltage values ​​measured when the pipe is empty and full of water, respectively. Step 3: Calculate the flow rate of the ultrasonic wet gas measurement by equation (2) : wherein, A A is the cross-sectional area of the pipe, L D is the distance between the two ultrasonic probes of the ultrasonic sensor, θ a is the angle between the ultrasonic sensor and the central axis of the pipe, c is a correction factor, c is 1.12; Step 4: Determine boundary values ​​and make judgments. RCD If RCD is less than the determined boundary value, proceed to step five if RCD is less than the boundary value, where the boundary value is 28.9%; otherwise, proceed to step six. Step 5: Determine if the pipe is a vertical pipe, if so, calculate the wet gas flow rate by equation (3) ; wherein is the fraction of the pipe cross-sectional area occupied by the centrally entrained droplets, and is the fraction of the pipe cross-sectional area occupied by the centrally entrained droplets, and is the fraction of the pipe cross-sectional area occupied by the centrally entrained droplets, and wherein Dp is the pipe diameter, is the liquid film thickness; If it is a horizontal pipe, the moisture gas flow rate is calculated by Equation (5) : wherein is half of the central angle of the gas-liquid interface corresponding circle, calculated from equation (6): wherein is the pipe radius, is the liquid film thickness, under the horizontal pipe is given by the equation: Step 6: When RCD greater than the boundary value, is determined by equation (8): wherein, and are coefficients to be fitted, is the liquid flow rate; determining whether the pipe is a vertical pipe, and if so, calculating the wet gas flow rate by simultaneously solving equations (4) and (8) .

2. The hydrogen circuit moisture flow measurement method of claim 1, wherein, In the sixth step, and 1.14 and 5.06, respectively.

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